1164 lines
33 KiB
Markdown
1164 lines
33 KiB
Markdown
|
|
|
|
# 30 seconds of code [](https://gitter.im/30-seconds-of-code/Lobby)
|
|
> Curated collection of useful Javascript snippets that you can understand in 30 seconds or less.
|
|
|
|
- Use <kbd>Ctrl</kbd> + <kbd>F</kbd> or <kbd>command</kbd> + <kbd>F</kbd> to search for a snippet.
|
|
- Contributions welcome, please read the [contribution guide](CONTRIBUTING.md).
|
|
- Snippets are written in ES6, use the [Babel transpiler](https://babeljs.io/) to ensure backwards-compatibility.
|
|
|
|
## Table of Contents
|
|
|
|
### Array
|
|
* [Array concatenation](#array-concatenation)
|
|
* [Array difference](#array-difference)
|
|
* [Array intersection](#array-intersection)
|
|
* [Array union](#array-union)
|
|
* [Average of array of numbers](#average-of-array-of-numbers)
|
|
* [Chunk array](#chunk-array)
|
|
* [Compact](#compact)
|
|
* [Count occurrences of a value in array](#count-occurrences-of-a-value-in-array)
|
|
* [Deep flatten array](#deep-flatten-array)
|
|
* [Drop elements in array](#drop-elements-in-array)
|
|
* [Fill array](#fill-array)
|
|
* [Filter out non unique values in an array](#filter-out-non-unique-values-in-an-array)
|
|
* [Flatten array up to depth](#flatten-array-up-to-depth)
|
|
* [Flatten array](#flatten-array)
|
|
* [Get max value from array](#get-max-value-from-array)
|
|
* [Get min value from array](#get-min-value-from-array)
|
|
* [Group by](#group-by)
|
|
* [Head of list](#head-of-list)
|
|
* [Initial of list](#initial-of-list)
|
|
* [Initialize array with range](#initialize-array-with-range)
|
|
* [Initialize array with values](#initialize-array-with-values)
|
|
* [Last of list](#last-of-list)
|
|
* [Median of array of numbers](#median-of-array-of-numbers)
|
|
* [Pick](#pick)
|
|
* [Shuffle array](#shuffle-array)
|
|
* [Similarity between arrays](#similarity-between-arrays)
|
|
* [Sum of array of numbers](#sum-of-array-of-numbers)
|
|
* [Tail of list](#tail-of-list)
|
|
* [Take](#take)
|
|
* [Unique values of array](#unique-values-of-array)
|
|
|
|
### Browser
|
|
* [Bottom visible](#bottom-visible)
|
|
* [Current URL](#current-url)
|
|
* [Element is visible in viewport](#element-is-visible-in-viewport)
|
|
* [Get scroll position](#get-scroll-position)
|
|
* [Redirect to URL](#redirect-to-url)
|
|
* [Scroll to top](#scroll-to-top)
|
|
|
|
### Function
|
|
* [Chain asynchronous functions](#chain-asynchronous-functions)
|
|
* [Curry](#curry)
|
|
* [Pipe](#pipe)
|
|
* [Promisify](#promisify)
|
|
* [Run promises in series](#run-promises-in-series)
|
|
* [Sleep](#sleep)
|
|
|
|
### Math
|
|
* [Collatz algorithm](#collatz-algorithm)
|
|
* [Distance between two points](#distance-between-two-points)
|
|
* [Divisible by number](#divisible-by-number)
|
|
* [Even or odd number](#even-or-odd-number)
|
|
* [Factorial](#factorial)
|
|
* [Fibonacci array generator](#fibonacci-array-generator)
|
|
* [Greatest common divisor (GCD)](#greatest-common-divisor-gcd)
|
|
* [Hamming distance](#hamming-distance)
|
|
* [Percentile](#percentile)
|
|
* [Powerset](#powerset)
|
|
* [Standard deviation](#standard-deviation)
|
|
|
|
### Object
|
|
* [Object from key value pairs](#object-from-key-value-pairs)
|
|
* [Object to key value pairs](#object-to-key-value-pairs)
|
|
|
|
### String
|
|
* [Anagrams of string (with duplicates)](#anagrams-of-string-with-duplicates)
|
|
* [Capitalize first letter of every word](#capitalize-first-letter-of-every-word)
|
|
* [Capitalize first letter](#capitalize-first-letter)
|
|
* [Check for palindrome](#check-for-palindrome)
|
|
* [Reverse a string](#reverse-a-string)
|
|
* [Sort characters in string (alphabetical)](#sort-characters-in-string-alphabetical)
|
|
* [Truncate a string](#truncate-a-string)
|
|
|
|
### Utility
|
|
* [Escape regular expression](#escape-regular-expression)
|
|
* [Get native type of value](#get-native-type-of-value)
|
|
* [Is array](#is-array)
|
|
* [Is boolean](#is-boolean)
|
|
* [Is function](#is-function)
|
|
* [Is number](#is-number)
|
|
* [Is string](#is-string)
|
|
* [Is symbol](#is-symbol)
|
|
* [Measure time taken by function](#measure-time-taken-by-function)
|
|
* [Ordinal suffix of number](#ordinal-suffix-of-number)
|
|
* [Random integer in range](#random-integer-in-range)
|
|
* [Random number in range](#random-number-in-range)
|
|
* [RGB to hexadecimal](#rgb-to-hexadecimal)
|
|
* [Swap values of two variables](#swap-values-of-two-variables)
|
|
* [URL parameters](#url-parameters)
|
|
* [UUID generator](#uuid-generator)
|
|
* [Validate email](#validate-email)
|
|
* [Validate number](#validate-number)
|
|
* [Value or default](#value-or-default)
|
|
|
|
## Array
|
|
|
|
### Array concatenation
|
|
|
|
Use `Array.concat()` to concatenate an array with any additional arrays and/or values, specified in `args`.
|
|
|
|
```js
|
|
const arrayConcat = (arr, ...args) => arr.concat(...args);
|
|
// arrayConcat([1], 2, [3], [[4]]) -> [1,2,3,[4]]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Array difference
|
|
|
|
Create a `Set` from `b`, then use `Array.filter()` on `a` to only keep values not contained in `b`.
|
|
|
|
```js
|
|
const difference = (a, b) => { const s = new Set(b); return a.filter(x => !s.has(x)); };
|
|
// difference([1,2,3], [1,2]) -> [3]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Array intersection
|
|
|
|
Create a `Set` from `b`, then use `Array.filter()` on `a` to only keep values contained in `b`.
|
|
|
|
```js
|
|
const intersection = (a, b) => { const s = new Set(b); return a.filter(x => s.has(x)); };
|
|
// intersection([1,2,3], [4,3,2]) -> [2,3]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Array union
|
|
|
|
Create a `Set` with all values of `a` and `b` and convert to an array.
|
|
|
|
```js
|
|
const union = (a, b) => Array.from(new Set([...a, ...b]));
|
|
// union([1,2,3], [4,3,2]) -> [1,2,3,4]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Average of array of numbers
|
|
|
|
Use `Array.reduce()` to add each value to an accumulator, initialized with a value of `0`, divide by the `length` of the array.
|
|
|
|
```js
|
|
const average = arr => arr.reduce((acc, val) => acc + val, 0) / arr.length;
|
|
// average([1,2,3]) -> 2
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Chunk array
|
|
|
|
Use `Array.from()` to create a new array, that fits the number of chunks that will be produced.
|
|
Use `Array.slice()` to map each element of the new array to a chunk the length of `size`.
|
|
If the original array can't be split evenly, the final chunk will contain the remaining elements.
|
|
|
|
```js
|
|
const chunk = (arr, size) =>
|
|
Array.from({length: Math.ceil(arr.length / size)}, (v, i) => arr.slice(i * size, i * size + size));
|
|
// chunk([1,2,3,4,5], 2) -> [[1,2],[3,4],5]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Compact
|
|
|
|
Use `Array.filter()` to filter out falsey values (`false`, `null`, `0`, `""`, `undefined`, and `NaN`).
|
|
|
|
```js
|
|
const compact = (arr) => arr.filter(v => v);
|
|
// compact([0, 1, false, 2, '', 3, 'a', 'e'*23, NaN, 's', 34]) -> [ 1, 2, 3, 'a', 's', 34 ]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Count occurrences of a value in array
|
|
|
|
Use `Array.reduce()` to increment a counter each time you encounter the specific value inside the array.
|
|
|
|
```js
|
|
const countOccurrences = (arr, value) => arr.reduce((a, v) => v === value ? a + 1 : a + 0, 0);
|
|
// countOccurrences([1,1,2,1,2,3], 1) -> 3
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Deep flatten array
|
|
|
|
Use recursion.
|
|
Use `Array.reduce()` to get all elements that are not arrays, flatten each element that is an array.
|
|
|
|
```js
|
|
const deepFlatten = arr =>
|
|
arr.reduce((a, v) => a.concat(Array.isArray(v) ? deepFlatten(v) : v), []);
|
|
// deepFlatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Drop elements in array
|
|
|
|
Loop through the array, using `Array.shift()` to drop the first element of the array until the returned value from the function is `true`.
|
|
Returns the remaining elements.
|
|
|
|
```js
|
|
const dropElements = (arr, func) => {
|
|
while (arr.length > 0 && !func(arr[0])) arr.shift();
|
|
return arr;
|
|
};
|
|
// dropElements([1, 2, 3, 4], n => n >= 3) -> [3,4]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Fill array
|
|
|
|
Use `Array.map()` to map values between `start` (inclusive) and `end` (exclusive) to `value`.
|
|
Omit `start` to start at the first element and/or `end` to finish at the last.
|
|
|
|
```js
|
|
const fillArray = (arr, value, start = 0, end = arr.length) =>
|
|
arr.map((v, i) => i >= start && i < end ? value : v);
|
|
// fillArray([1,2,3,4],'8',1,3) -> [1,'8','8',4]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Filter out non-unique values in an array
|
|
|
|
Use `Array.filter()` for an array containing only the unique values.
|
|
|
|
```js
|
|
const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
|
|
// filterNonUnique([1,2,2,3,4,4,5]) -> [1,3,5]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Flatten array up to depth
|
|
|
|
Use recursion, decrementing `depth` by 1 for each level of depth.
|
|
Use `Array.reduce()` and `Array.concat()` to merge elements or arrays.
|
|
Base case, for `depth` equal to `1` stops recursion.
|
|
Omit the second element, `depth` to flatten only to a depth of `1` (single flatten).
|
|
|
|
```js
|
|
const flattenDepth = (arr, depth = 1) =>
|
|
depth != 1 ? arr.reduce((a, v) => a.concat(Array.isArray(v) ? flattenDepth(v, depth - 1) : v), [])
|
|
: arr.reduce((a, v) => a.concat(v), []);
|
|
// flattenDepth([1,[2],[[[3],4],5]], 2) -> [1,2,[3],4,5]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Flatten array
|
|
|
|
Use `Array.reduce()` to get all elements inside the array and `concat()` to flatten them.
|
|
|
|
```js
|
|
const flatten = arr => arr.reduce((a, v) => a.concat(v), []);
|
|
// flatten([1,[2],3,4]) -> [1,2,3,4]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Get max value from array
|
|
|
|
Use `Math.max()` combined with the spread operator (`...`) to get the maximum value in the array.
|
|
|
|
```js
|
|
const arrayMax = arr => Math.max(...arr);
|
|
// arrayMax([10, 1, 5]) -> 10
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Get min value from array
|
|
|
|
Use `Math.min()` combined with the spread operator (`...`) to get the minimum value in the array.
|
|
|
|
```js
|
|
const arrayMin = arr => Math.min(...arr);
|
|
// arrayMin([10, 1, 5]) -> 1
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Group by
|
|
|
|
Use `Array.map()` to map the values of an array to a function or property name.
|
|
Use `Array.reduce()` to create an object, where the keys are produced from the mapped results.
|
|
|
|
```js
|
|
const groupBy = (arr, func) =>
|
|
arr.map(typeof func === 'function' ? func : val => val[func])
|
|
.reduce((acc, val, i) => { acc[val] = (acc[val] || []).concat(arr[i]); return acc; }, {});
|
|
// groupBy([6.1, 4.2, 6.3], Math.floor) -> {4: [4.2], 6: [6.1, 6.3]}
|
|
// groupBy(['one', 'two', 'three'], 'length') -> {3: ['one', 'two'], 5: ['three']}
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Head of list
|
|
|
|
Use `arr[0]` to return the first element of the passed array.
|
|
|
|
```js
|
|
const head = arr => arr[0];
|
|
// head([1,2,3]) -> 1
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Initial of list
|
|
|
|
Use `arr.slice(0,-1)`to return all but the last element of the array.
|
|
|
|
```js
|
|
const initial = arr => arr.slice(0, -1);
|
|
// initial([1,2,3]) -> [1,2]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Initialize array with range
|
|
|
|
Use `Array(end-start)` to create an array of the desired length, `Array.map()` to fill with the desired values in a range.
|
|
You can omit `start` to use a default value of `0`.
|
|
|
|
```js
|
|
const initializeArrayRange = (end, start = 0) =>
|
|
Array.apply(null, Array(end - start)).map((v, i) => i + start);
|
|
// initializeArrayRange(5) -> [0,1,2,3,4]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Initialize array with values
|
|
|
|
Use `Array(n)` to create an array of the desired length, `fill(v)` to fill it with the desired values.
|
|
You can omit `value` to use a default value of `0`.
|
|
|
|
```js
|
|
const initializeArray = (n, value = 0) => Array(n).fill(value);
|
|
// initializeArray(5, 2) -> [2,2,2,2,2]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Last of list
|
|
|
|
Use `arr.slice(-1)[0]` to get the last element of the given array.
|
|
|
|
```js
|
|
const last = arr => arr.slice(-1)[0];
|
|
// last([1,2,3]) -> 3
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Median of array of numbers
|
|
|
|
Find the middle of the array, use `Array.sort()` to sort the values.
|
|
Return the number at the midpoint if `length` is odd, otherwise the average of the two middle numbers.
|
|
|
|
```js
|
|
const median = arr => {
|
|
const mid = Math.floor(arr.length / 2), nums = arr.sort((a, b) => a - b);
|
|
return arr.length % 2 !== 0 ? nums[mid] : (nums[mid - 1] + nums[mid]) / 2;
|
|
};
|
|
// median([5,6,50,1,-5]) -> 5
|
|
// median([0,10,-2,7]) -> 3.5
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Pick
|
|
|
|
Use `Array.reduce()` to convert the filtered/picked keys back to a object with the corresponding key:value pair if the key exist in the obj.
|
|
|
|
```js
|
|
const pick = (obj, arr) =>
|
|
arr.reduce((acc, curr) => (curr in obj && (acc[curr] = obj[curr]), acc), {});
|
|
// pick({ 'a': 1, 'b': '2', 'c': 3 }, ['a', 'c']) -> { 'a': 1, 'c': 3 }
|
|
// pick(object, ['a', 'c'])['a'] -> 1
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Shuffle array
|
|
|
|
Use `Array.sort()` to reorder elements, using `Math.random()` in the comparator.
|
|
|
|
```js
|
|
const shuffle = arr => arr.sort(() => Math.random() - 0.5);
|
|
// shuffle([1,2,3]) -> [2,3,1]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Similarity between arrays
|
|
|
|
Use `filter()` to remove values that are not part of `values`, determined using `includes()`.
|
|
|
|
```js
|
|
const similarity = (arr, values) => arr.filter(v => values.includes(v));
|
|
// similarity([1,2,3], [1,2,4]) -> [1,2]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Sum of array of numbers
|
|
|
|
Use `Array.reduce()` to add each value to an accumulator, initialized with a value of `0`.
|
|
|
|
```js
|
|
const sum = arr => arr.reduce((acc, val) => acc + val, 0);
|
|
// sum([1,2,3,4]) -> 10
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Tail of list
|
|
|
|
Return `arr.slice(1)` if the array's `length` is more than `1`, otherwise return the whole array.
|
|
|
|
```js
|
|
const tail = arr => arr.length > 1 ? arr.slice(1) : arr;
|
|
// tail([1,2,3]) -> [2,3]
|
|
// tail([1]) -> [1]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Take
|
|
|
|
Use `Array.slice()` to create a slice of the array with `n` elements taken from the beginning.
|
|
|
|
```js
|
|
const take = (arr, n = 1) => arr.slice(0, n);
|
|
// take([1, 2, 3], 5) -> [1, 2, 3]
|
|
// take([1, 2, 3], 0) -> []
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Unique values of array
|
|
|
|
Use ES6 `Set` and the `...rest` operator to discard all duplicated values.
|
|
|
|
```js
|
|
const unique = arr => [...new Set(arr)];
|
|
// unique([1,2,2,3,4,4,5]) -> [1,2,3,4,5]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
## Browser
|
|
|
|
### Bottom visible
|
|
|
|
Use `scrollY`, `scrollHeight` and `clientHeight` to determine if the bottom of the page is visible.
|
|
|
|
```js
|
|
const bottomVisible = _ =>
|
|
document.documentElement.clientHeight + window.scrollY >= document.documentElement.scrollHeight || document.documentElement.clientHeight;
|
|
// bottomVisible() -> true
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Current URL
|
|
|
|
Use `window.location.href` to get current URL.
|
|
|
|
```js
|
|
const currentUrl = _ => window.location.href;
|
|
// currentUrl() -> 'https://google.com'
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Element is visible in viewport
|
|
|
|
Use `Element.getBoundingClientRect()` and the `window.inner(Width|Height)` values
|
|
to determine if a given element is visible in the viewport.
|
|
Omit the second argument to determine if the element is entirely visible, or specify `true` to determine if
|
|
it is partially visible.
|
|
|
|
```js
|
|
const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
|
|
const { top, left, bottom, right } = el.getBoundingClientRect();
|
|
return partiallyVisible
|
|
? ((top > 0 && top < innerHeight) || (bottom > 0 && bottom < innerHeight)) &&
|
|
((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
|
|
: top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
|
|
};
|
|
// e.g. 100x100 viewport and a 10x10px element at position {top: -1, left: 0, bottom: 9, right: 10}
|
|
// elementIsVisibleInViewport(el) -> false (not fully visible)
|
|
// elementIsVisibleInViewport(el, true) -> true (partially visible)
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Get scroll position
|
|
|
|
Use `pageXOffset` and `pageYOffset` if they are defined, otherwise `scrollLeft` and `scrollTop`.
|
|
You can omit `el` to use a default value of `window`.
|
|
|
|
```js
|
|
const getScrollPos = (el = window) =>
|
|
({x: (el.pageXOffset !== undefined) ? el.pageXOffset : el.scrollLeft,
|
|
y: (el.pageYOffset !== undefined) ? el.pageYOffset : el.scrollTop});
|
|
// getScrollPos() -> {x: 0, y: 200}
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Redirect to URL
|
|
|
|
Use `window.location.href` or `window.location.replace()` to redirect to `url`.
|
|
Pass a second argument to simulate a link click (`true` - default) or an HTTP redirect (`false`).
|
|
|
|
```js
|
|
const redirect = (url, asLink = true) =>
|
|
asLink ? window.location.href = url : window.location.replace(url);
|
|
// redirect('https://google.com')
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Scroll to top
|
|
|
|
Get distance from top using `document.documentElement.scrollTop` or `document.body.scrollTop`.
|
|
Scroll by a fraction of the distance from top. Use `window.requestAnimationFrame()` to animate the scrolling.
|
|
|
|
```js
|
|
const scrollToTop = _ => {
|
|
const c = document.documentElement.scrollTop || document.body.scrollTop;
|
|
if (c > 0) {
|
|
window.requestAnimationFrame(scrollToTop);
|
|
window.scrollTo(0, c - c / 8);
|
|
}
|
|
};
|
|
// scrollToTop()
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
## Function
|
|
|
|
### Chain asynchronous functions
|
|
|
|
Loop through an array of functions containing asynchronous events, calling `next` when each asynchronous event has completed.
|
|
|
|
```js
|
|
const chainAsync = fns => { let curr = 0; const next = () => fns[curr++](next); next(); };
|
|
/*
|
|
chainAsync([
|
|
next => { console.log('0 seconds'); setTimeout(next, 1000); },
|
|
next => { console.log('1 second'); setTimeout(next, 1000); },
|
|
next => { console.log('2 seconds'); }
|
|
])
|
|
*/
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Curry
|
|
|
|
Use recursion.
|
|
If the number of provided arguments (`args`) is sufficient, call the passed function `f`.
|
|
Otherwise return a curried function `f` that expects the rest of the arguments.
|
|
If you want to curry a function that accepts a variable number of arguments (a variadic function, e.g. `Math.min()`), you can optionally pass the number of arguments to the second parameter `arity`.
|
|
|
|
```js
|
|
const curry = (fn, arity = fn.length, ...args) =>
|
|
arity <= args.length
|
|
? fn(...args)
|
|
: curry.bind(null, fn, arity, ...args)
|
|
// curry(Math.pow)(2)(10) -> 1024
|
|
// curry(Math.min, 3)(10)(50)(2) -> 2
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Pipe
|
|
|
|
Use `Array.reduce()` to pass value through functions.
|
|
|
|
```js
|
|
const pipe = (...funcs) => arg => funcs.reduce((acc, func) => func(acc), arg);
|
|
// pipe(btoa, x => x.toUpperCase())("Test") -> "VGVZDA=="
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Promisify
|
|
|
|
Use currying to return a function returning a `Promise` that calls the original function.
|
|
Use the `...rest` operator to pass in all the parameters.
|
|
|
|
*In Node 8+, you can use [`util.promisify`](https://nodejs.org/api/util.html#util_util_promisify_original)*
|
|
|
|
```js
|
|
const promisify = func =>
|
|
(...args) =>
|
|
new Promise((resolve, reject) =>
|
|
func(...args, (err, result) =>
|
|
err ? reject(err) : resolve(result))
|
|
);
|
|
// const delay = promisify((d, cb) => setTimeout(cb, d))
|
|
// delay(2000).then(() => console.log('Hi!')) -> Promise resolves after 2s
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Run promises in series
|
|
|
|
Run an array of promises in series using `Array.reduce()` by creating a promise chain, where each promise returns the next promise when resolved.
|
|
|
|
```js
|
|
const series = ps => ps.reduce((p, next) => p.then(next), Promise.resolve());
|
|
// const delay = (d) => new Promise(r => setTimeout(r, d))
|
|
// series([() => delay(1000), () => delay(2000)]) -> executes each promise sequentially, taking a total of 3 seconds to complete
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Sleep
|
|
|
|
Delay executing part of an `async` function, by putting it to sleep, returning a `Promise`.
|
|
|
|
```js
|
|
const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
|
|
/*
|
|
async function sleepyWork() {
|
|
console.log('I\'m going to sleep for 1 second.');
|
|
await sleep(1000);
|
|
console.log('I woke up after 1 second.');
|
|
}
|
|
*/
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
## Math
|
|
|
|
### Collatz algorithm
|
|
|
|
If `n` is even, return `n/2`. Otherwise return `3n+1`.
|
|
|
|
```js
|
|
const collatz = n => (n % 2 == 0) ? (n / 2) : (3 * n + 1);
|
|
// collatz(8) --> 4
|
|
// collatz(5) --> 16
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Distance between two points
|
|
|
|
Use `Math.hypot()` to calculate the Euclidean distance between two points.
|
|
|
|
```js
|
|
const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);
|
|
// distance(1,1, 2,3) -> 2.23606797749979
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Divisible by number
|
|
|
|
Use the modulo operator (`%`) to check if the remainder is equal to `0`.
|
|
|
|
```js
|
|
const isDivisible = (dividend, divisor) => dividend % divisor === 0;
|
|
// isDivisible(6,3) -> true
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Even or odd number
|
|
|
|
Checks whether a number is odd or even using the modulo (`%`) operator.
|
|
Returns `true` if the number is even, `false` if the number is odd.
|
|
|
|
```js
|
|
const isEven = num => num % 2 === 0;
|
|
// isEven(3) -> false
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Factorial
|
|
|
|
Use recursion.
|
|
If `n` is less than or equal to `1`, return `1`.
|
|
Otherwise, return the product of `n` and the factorial of `n - 1`.
|
|
|
|
```js
|
|
const factorial = n => n <= 1 ? 1 : n * factorial(n - 1);
|
|
// factorial(6) -> 720
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Fibonacci array generator
|
|
|
|
Create an empty array of the specific length, initializing the first two values (`0` and `1`).
|
|
Use `Array.reduce()` to add values into the array, using the sum of the last two values, except for the first two.
|
|
|
|
```js
|
|
const fibonacci = n =>
|
|
Array(n).fill(0).reduce((acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i), []);
|
|
// fibonacci(5) -> [0,1,1,2,3]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Greatest common divisor (GCD)
|
|
|
|
Use recursion.
|
|
Base case is when `y` equals `0`. In this case, return `x`.
|
|
Otherwise, return the GCD of `y` and the remainder of the division `x/y`.
|
|
|
|
```js
|
|
const gcd = (x, y) => !y ? x : gcd(y, x % y);
|
|
// gcd (8, 36) -> 4
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Hamming distance
|
|
|
|
Use XOR operator (`^`) to find the bit difference between the two numbers, convert to binary string using `toString(2)`.
|
|
Count and return the number of `1`s in the string, using `match(/1/g)`.
|
|
|
|
```js
|
|
const hammingDistance = (num1, num2) =>
|
|
((num1 ^ num2).toString(2).match(/1/g) || '').length;
|
|
// hammingDistance(2,3) -> 1
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Percentile
|
|
|
|
Use `Array.reduce()` to calculate how many numbers are below the value and how many are the same value and
|
|
apply the percentile formula.
|
|
|
|
```js
|
|
const percentile = (arr, val) =>
|
|
100 * arr.reduce((acc,v) => acc + (v < val ? 1 : 0) + (v === val ? 0.5 : 0), 0) / arr.length;
|
|
// percentile([1,2,3,4,5,6,7,8,9,10], 6) -> 55
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Powerset
|
|
|
|
Use `Array.reduce()` combined with `Array.map()` to iterate over elements and combine into an array containing all combinations.
|
|
|
|
```js
|
|
const powerset = arr =>
|
|
arr.reduce((a, v) => a.concat(a.map(r => [v].concat(r))), [[]]);
|
|
// powerset([1,2]) -> [[], [1], [2], [2,1]]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Standard deviation
|
|
|
|
Use `Array.reduce()` to calculate the mean, variance and the sum of the variance of the values, the variance of the values, then
|
|
determine the standard deviation.
|
|
You can omit the second argument to get the sample standard deviation or set it to `true` to get the population standard deviation.
|
|
|
|
```js
|
|
const standardDeviation = (arr, usePopulation = false) => {
|
|
const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
|
|
return Math.sqrt(
|
|
arr.reduce((acc, val) => acc.concat(Math.pow(val - mean, 2)), [])
|
|
.reduce((acc, val) => acc + val, 0) / (arr.length - (usePopulation ? 0 : 1))
|
|
);
|
|
};
|
|
// standardDeviation([10,2,38,23,38,23,21]) -> 13.284434142114991 (sample)
|
|
// standardDeviation([10,2,38,23,38,23,21], true) -> 12.29899614287479 (population)
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
## Object
|
|
|
|
### Object from key-value pairs
|
|
|
|
Use `Array.reduce()` to create and combine key-value pairs.
|
|
|
|
```js
|
|
const objectFromPairs = arr => arr.reduce((a, v) => (a[v[0]] = v[1], a), {});
|
|
// objectFromPairs([['a',1],['b',2]]) -> {a: 1, b: 2}
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Object to key-value pairs
|
|
|
|
Use `Object.keys()` and `Array.map()` to iterate over the object's keys and produce an array with key-value pairs.
|
|
|
|
```js
|
|
const objectToPairs = obj => Object.keys(obj).map(k => [k, obj[k]]);
|
|
// objectToPairs({a: 1, b: 2}) -> [['a',1],['b',2]])
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
## String
|
|
|
|
### Anagrams of string (with duplicates)
|
|
|
|
Use recursion.
|
|
For each letter in the given string, create all the partial anagrams for the rest of its letters.
|
|
Use `Array.map()` to combine the letter with each partial anagram, then `Array.reduce()` to combine all anagrams in one array.
|
|
Base cases are for string `length` equal to `2` or `1`.
|
|
|
|
```js
|
|
const anagrams = str => {
|
|
if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
|
|
return str.split('').reduce((acc, letter, i) =>
|
|
acc.concat(anagrams(str.slice(0, i) + str.slice(i + 1)).map(val => letter + val)), []);
|
|
};
|
|
// anagrams('abc') -> ['abc','acb','bac','bca','cab','cba']
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Capitalize first letter of every word
|
|
|
|
Use `replace()` to match the first character of each word and `toUpperCase()` to capitalize it.
|
|
|
|
```js
|
|
const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());
|
|
// capitalizeEveryWord('hello world!') -> 'Hello World!'
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Capitalize first letter
|
|
|
|
Use `slice(0,1)` and `toUpperCase()` to capitalize first letter, `slice(1)` to get the rest of the string.
|
|
Omit the `lowerRest` parameter to keep the rest of the string intact, or set it to `true` to convert to lower case.
|
|
|
|
```js
|
|
const capitalize = (str, lowerRest = false) =>
|
|
str.slice(0, 1).toUpperCase() + (lowerRest ? str.slice(1).toLowerCase() : str.slice(1));
|
|
// capitalize('myName', true) -> 'Myname'
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Check for palindrome
|
|
|
|
Convert string `toLowerCase()` and use `replace()` to remove non-alphanumeric characters from it.
|
|
Then, `split('')` into individual characters, `reverse()`, `join('')` and compare to the original, unreversed string, after converting it `tolowerCase()`.
|
|
|
|
```js
|
|
const palindrome = str => {
|
|
const s = str.toLowerCase().replace(/[\W_]/g,'');
|
|
return s === s.split('').reverse().join('');
|
|
}
|
|
// palindrome('taco cat') -> true
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Reverse a string
|
|
|
|
Use array destructuring and `Array.reverse()` to reverse the order of the characters in the string.
|
|
Combine characters to get a string using `join('')`.
|
|
|
|
```js
|
|
const reverseString = str => [...str].reverse().join('');
|
|
// reverseString('foobar') -> 'raboof'
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Sort characters in string (alphabetical)
|
|
|
|
Split the string using `split('')`, `Array.sort()` utilizing `localeCompare()`, recombine using `join('')`.
|
|
|
|
```js
|
|
const sortCharactersInString = str =>
|
|
str.split('').sort((a, b) => a.localeCompare(b)).join('');
|
|
// sortCharactersInString('cabbage') -> 'aabbceg'
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Truncate a String
|
|
|
|
Determine if the string's `length` is greater than `num`.
|
|
Return the string truncated to the desired length, with `...` appended to the end or the original string.
|
|
|
|
```js
|
|
const truncate = (str, num) =>
|
|
str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + '...' : str;
|
|
// truncate('boomerang', 7) -> 'boom...'
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
## Utility
|
|
|
|
### Escape regular expression
|
|
|
|
Use `replace()` to escape special characters.
|
|
|
|
```js
|
|
const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
|
|
// escapeRegExp('(test)') -> \\(test\\)
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Get native type of value
|
|
|
|
Returns lower-cased constructor name of value, "undefined" or "null" if value is undefined or null
|
|
|
|
```js
|
|
const getType = v =>
|
|
v === undefined ? 'undefined' : v === null ? 'null' : v.constructor.name.toLowerCase();
|
|
// getType(new Set([1,2,3])) -> "set"
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Is array
|
|
|
|
Use `Array.isArray()` to check if a value is classified as an array.
|
|
|
|
```js
|
|
const isArray = val => val && Array.isArray(val);
|
|
// isArray(null) -> false
|
|
// isArray([1]) -> true
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Is boolean
|
|
|
|
Use `typeof` to check if a value is classified as a boolean primitive.
|
|
|
|
```js
|
|
const isBoolean = val => typeof val === 'boolean';
|
|
// isBoolean(null) -> false
|
|
// isBoolean(false) -> true
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Is function
|
|
|
|
Use `typeof` to check if a value is classified as a function primitive.
|
|
|
|
```js
|
|
const isFunction = val => val && typeof val === 'function';
|
|
// isFunction('x') -> false
|
|
// isFunction(x => x) -> true
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Is number
|
|
|
|
Use `typeof` to check if a value is classified as a number primitive.
|
|
|
|
```js
|
|
const isNumber = val => typeof val === 'number';
|
|
// isNumber('1') -> false
|
|
// isNumber(1) -> true
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Is string
|
|
|
|
Use `typeof` to check if a value is classified as a string primitive.
|
|
|
|
```js
|
|
const isString = val => typeof val === 'string';
|
|
// isString(10) -> false
|
|
// isString('10') -> true
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Is symbol
|
|
|
|
Use `typeof` to check if a value is classified as a symbol primitive.
|
|
|
|
```js
|
|
const isSymbol = val => typeof val === 'symbol';
|
|
// isSymbol('x') -> false
|
|
// isSymbol(Symbol('x')) -> true
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Measure time taken by function
|
|
|
|
Use `performance.now()` to get start and end time for the function, `console.log()` the time taken.
|
|
Pass a callback function as the argument.
|
|
|
|
```js
|
|
const timeTaken = callback => {
|
|
const t0 = performance.now(), r = callback();
|
|
console.log(performance.now() - t0);
|
|
return r;
|
|
};
|
|
// timeTaken(() => Math.pow(2, 10)) -> 1024 (0.010000000009313226 logged in console)
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Ordinal suffix of number
|
|
|
|
Use the modulo operator (`%`) to find values of single and tens digits.
|
|
Find which ordinal pattern digits match.
|
|
If digit is found in teens pattern, use teens ordinal.
|
|
|
|
```js
|
|
const toOrdinalSuffix = num => {
|
|
const int = parseInt(num), digits = [(int % 10), (int % 100)],
|
|
ordinals = ['st', 'nd', 'rd', 'th'], oPattern = [1, 2, 3, 4],
|
|
tPattern = [11, 12, 13, 14, 15, 16, 17, 18, 19];
|
|
return oPattern.includes(digits[0]) && !tPattern.includes(digits[1]) ? int + ordinals[digits[0] - 1] : int + ordinals[3];
|
|
};
|
|
// toOrdinalSuffix("123") -> "123rd"
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Random integer in range
|
|
|
|
Use `Math.random()` to generate a random number and map it to the desired range, using `Math.floor()` to make it an integer.
|
|
|
|
```js
|
|
const randomIntegerInRange = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;
|
|
// randomIntegerInRange(0, 5) -> 2
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Random number in range
|
|
|
|
Use `Math.random()` to generate a random value, map it to the desired range using multiplication.
|
|
|
|
```js
|
|
const randomInRange = (min, max) => Math.random() * (max - min) + min;
|
|
// randomInRange(2,10) -> 6.0211363285087005
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### RGB to hexadecimal
|
|
|
|
Convert given RGB parameters to hexadecimal string using bitwise left-shift operator (`<<`) and `toString(16)`, then `padStart(6,'0')` to get a 6-digit hexadecimal value.
|
|
|
|
```js
|
|
const rgbToHex = (r, g, b) => ((r << 16) + (g << 8) + b).toString(16).padStart(6, '0');
|
|
// rgbToHex(255, 165, 1) -> 'ffa501'
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Swap values of two variables
|
|
|
|
Use array destructuring to swap values between two variables.
|
|
|
|
```js
|
|
[varA, varB] = [varB, varA];
|
|
// [x, y] = [y, x]
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### URL parameters
|
|
|
|
Use `match()` with an appropriate regular expression to get all key-value pairs, `Array.reduce()` to map and combine them into a single object.
|
|
Pass `location.search` as the argument to apply to the current `url`.
|
|
|
|
```js
|
|
const getUrlParameters = url =>
|
|
url.match(/([^?=&]+)(=([^&]*))/g).reduce(
|
|
(a, v) => (a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1), a), {}
|
|
);
|
|
// getUrlParameters('http://url.com/page?name=Adam&surname=Smith') -> {name: 'Adam', surname: 'Smith'}
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### UUID generator
|
|
|
|
Use `crypto` API to generate a UUID, compliant with [RFC4122](https://www.ietf.org/rfc/rfc4122.txt) version 4.
|
|
|
|
```js
|
|
const uuid = _ =>
|
|
([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
|
|
(c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
|
|
);
|
|
// uuid() -> '7982fcfe-5721-4632-bede-6000885be57d'
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Validate email
|
|
|
|
Use a regular experssion to check if the email is valid.
|
|
Returns `true` if email is valid, `false` if not.
|
|
|
|
```js
|
|
const validateEmail = str =>
|
|
/^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/.test(str);
|
|
// validateEmail(mymail@gmail.com) -> true
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Validate number
|
|
|
|
Use `!isNaN` in combination with `parseFloat()` to check if the argument is a number.
|
|
Use `isFinite()` to check if the number is finite.
|
|
Use `Number()` to check if the coercion holds.
|
|
|
|
```js
|
|
const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n) && Number(n) == n;
|
|
// validateNumber('10') -> true
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
### Value or default
|
|
|
|
Returns value, or default value if passed value is `falsy`.
|
|
|
|
```js
|
|
const valueOrDefault = (value, d) => value || d;
|
|
// valueOrDefault(NaN, 30) -> 30
|
|
```
|
|
|
|
[⬆ back to top](#table-of-contents)
|
|
|
|
## Credits
|
|
|
|
*Icons made by [Smashicons](https://www.flaticon.com/authors/smashicons) from [www.flaticon.com](https://www.flaticon.com/) is licensed by [CC 3.0 BY](http://creativecommons.org/licenses/by/3.0/).*
|
|
|